Orbital magnetism in ultrathin films of CoFeB and its control by spin current

We present experimental evidence for orbital magnetism in ultrathin films of amorphous ferromagnet Co₄₀Fe₄₀B₂₀. Magnetoelectronic measurements based on the anomalous Hall effect (AHE) show a significant nonlinear contribution separate from the usual paramagnetic response, characterized by a different dependence on temperature and an opposite sign of AHE. A similar nonlinear feature is observed in current-biased microstructures in the ferromagnetic state. Brillouin Light Spectroscopy of thermal magnetization fluctuations reveals a strong current dependence of the Lande g-factor and the magnetic anisotropy on current, consistent with a large current-dependent orbital moment. We utilize a Hubbard model complemented with a two-order-parameter Landau theory of phase transition to demonstrate that the observed anomalous behaviors can be explained by the ferromagnetic orbital correlations associated with orbitally selective electron hopping confined to the film plane. This mechanism allows for efficient control of magnetic and magnetoelectronic properties of thin films via electron correlations.